The present invention relates to a radiation detector and a radiation apparatus.
In recent years, the ionizing radiation has been detected mainly by use of a semiconductor element. The radiation is transformed into positive holes and electrons by the semiconductor element. A cathode and an anode are formed on the surface of the semiconductor element, and the positive holes and the electrons are detected by applying a voltage between the cathode and the anode. Specifically, an electric field is formed between the cathode and the anode, and the positive holes and the electrons are moved toward the cathode and the anode, respectively. With the movement of the positive holes and the electrons, the voltages induced in the cathode and the anode are detected.
The electrons and the positive holes have a mean life unique to the base material of the semiconductor. Especially, the positive holes tend to become extinguished within a comparatively short time. In the case where a signal is acquired in a given electrode, another electrode having a constant potential arranged around the given electrode can shield the charge induced in the signal-acquiring electrode due to the movement of the charge outside the second electrode. In view of this, a technique has been conceived in which an electrode is arranged in the neighborhood of an anode as a shield electrode impressed with a voltage intermediate the anode voltage and the cathode voltage. The shield electrode is often called a Frisch grid electrode. The structure of this electrode makes it possible to detect the positive holes comparatively efficiently even in the case where they are extinguished within a short time. This technique is described, for example, in JP-A-9-171081, JP-A-2000-121738 or JP-A-10-512372.